756 THE JOURNAL OF GEOLOGY. 



ous citations are given showing that the general attitude of American geolo- 

 gists has been against the recognition of chalk in the American Cretaceous. 

 " The characteristics of the Niobrara chalk are such that exhaustive inves- 

 tigations with the microscope may be carried out with very little difficulty." 

 Foraminifera are abundant, and in places constitute from one fourth to one 

 third the volume of the chalk. Coccoliths are most abundant, though the 

 small, rodlike rhabdoliths may also be detected with a high-power objective. 

 The genera and species represented vary somewhat with the locality and the 

 beds from which they were obtained. Textularia globosa is represented by a 

 large and a small form, which grade into each other. The latter has been 

 regarded as a distinct species, Textularia pygmcza, by Dawson. Differences in 

 development are correlated with the probable conditions relative to depth and 

 the amount of earthy sediments. The identity of the Niobrara with the English 

 chalk is well established. C. H. G. 



A Study of the Cherts of Missouri. E. O. Hovey. (American Journal 

 of Science, November, 1894, p. 401.) 



Thirty-eight specimens from different parts of the state were examined in 

 fifty thin sections, about one-half from the Lower Magnesian (Ozark of Broad- 

 head) Series, and about one-half from the Lower Carboniferous. 



Petrography and fossil remains. — The cherts consist mostly of chalcedony, 

 with quartz and opal present to some extent. Careful search failed to reveal 

 any indication of radiolaria or sponge spicules, with the exception of certain 

 slender, cylindrical rods in one specimen, which showed nuclei of a brown 

 substance surrounded by clear chalcedony. Many of the fossiliferous cherts 

 from the Lower Carboniferous showed sections of brachiopods, crinoids, and 

 corals, and in some cases of Stromatopora. 



Chemistry. — Analyses showed the non-fossiliferous cherts to be nearly 

 pure silica with more or less alumina and iron. The "altered" and "unal- 

 tered" cherts are shown to be chemically very nearly identical. The very 

 small percentage of water in the pure cherts would indicate a srriall amount 

 of opal. 



Origin. — The theories of Prestwich, Hull, and Hardman, Irving and Van 

 Hise, Renard and Hinde are reviewed, and the author concludes that the cherts 

 studied by him "are due to chemical precipitation, probably at the time of 

 the deposition of the strata in which they occur, or before their consolida- 

 tion." E. C. Q. 



